The present invention relates in general to band gap references and, more particularly, to bypassed band gap references with current feedback.
Stable reference voltages are commonly used in electronic devices such as comparison circuits and analog to digital conversion circuits. The stable reference is required to achieve a high degree of accuracy when using the reference voltage, for example, as a first input to a comparator. The second input to the comparator is used to receive a signal used to compare against the reference voltage. A logic one, for example, is provided by the comparator if the input signal is above the reference voltage and a logic zero, for example, is provided by the comparator if the input signal is below the reference voltage. In many applications, the comparison performed by the comparator circuit must be as accurate as possible. One contributing factor to the inaccuracy of the comparison is, for example, noise contributed by the band gap reference itself.
Prior art band gap references provide an external bypass capacitor to reduce the noise level of the reference. Using a bypass capacitor, however, creates a system which takes a substantial amount of time to become stable, due to the charging requirements of the bypass capacitor. Other prior art reference circuits provide a pre-charge block which pre-charges the bypass capacitor to decrease the amount of time required to produce a stable reference voltage. Such prior art designs, however, require comparators, switches and miscellaneous additional circuitry to sense that the bypass capacitor is charged, so that the charging signal is terminated upon creating an acceptable charge across the bypass capacitor. The sensing circuitry increases the complexity of the reference voltage design and increases the quiescent current which is generally an issue in low power designs.
Hence, there is a need for a band gap reference circuit which provides reduced noise and fast response without the additional sensing circuitry.